In recent years, a biometric authentication technique has been developed in which a user of an apparatus or a system is authenticated based on a biometric image representing biometric information such as a vein pattern of a hand or a finger, a fingerprint, or a palm print. In a biometric authentication apparatus utilizing such a biometric authentication technique, for example, a biometric information capturing apparatus acquires a biometric image representing biometric information by capturing a body part including the biometric information of a user intending to use the biometric authentication apparatus. The biometric authentication apparatus matches the input biometric information which is the biometric information of the user represented in the biometric image, to registered biometric information which is biometric information represented in biometric image of a registered user registered in advance. When the input biometric information and the registered biometric information are determined to be in coincidence based on a result of a matching process, the biometric authentication apparatus authenticates the user as the registered user having a valid authority. The biometric authentication apparatus allows the authenticated user to use an apparatus in which the biometric authentication apparatus is incorporated or other apparatus connected to the biometric authentication apparatus.
When biometric information is a vein pattern of a palm or a finger, a light emitting element emitting near-infrared light such as an infrared LED is used as an illumination light source for allowing the illumination light to reach into the inside of a hand or a finger. In order to generate an image in which a vein pattern is captured by detecting illumination light reflected or scattered by a hand or a finger, which is an object to be captured, or transmitted through the object to be captured, a biometric information image capturing apparatus uses an image sensor in which sensor elements having sensitivity to near-infrared light are arranged in two dimensions. As the sensor elements, a solid-state image capturing element such as a charge-coupled device (CCD) or a Complementary Metal Oxide Semiconductor (CMOS) are utilized, for example.
However, an image sensor for near-infrared light is generally more expensive than an image sensor for visible light since the image sensor for near-infrared light is used in special applications and is not mass-produced. Although a CCD and a CMOS are image sensors for visible light, the CCD and CMOS also have sensitivity to near-infrared light. Thus, if an image sensor for visible light can be used for capturing a vein pattern, it is possible to reduce the cost of a biometric information image capturing apparatus. However, since a CCD and a CMOS do not have a function for identifying color, the image sensor for visible light, a color image sensor in particular, generally include, for each sensor element, a color filter which a light of a specific wavelength passes through. For example, sensor elements of two columns by two rows are formed as one set, and filters which a light of a wavelength corresponding to green passes through are arranged at two sensor elements along one of the diagonal lines. At the other two sensor elements, a filter through which a light of wavelength corresponding to red passes and a filter through which a light of wavelength corresponding to blue passes are respectively arranged. Such an array of filters is referred to as a Bayer array.
An image capturing apparatus is proposed in which one filter for green among filters in which such four sensor elements are grouped into a set is replaced with a filter for near-infrared light and an inside of a human body is an object to be captured, the human body being illuminated with near-infrared light (for example, Japanese Laid-open Patent Publication No. 2005-191748).